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From the micromagnetic simulation, it is found that the size-dependent stably existing regions of quasiuniform∕flower state, C, S, and vortex states are different in thin circular and square Permalloy dots. In very small dot’s size, the quasiuniform∕flower state is the most stable state both in circular and square Permalloy dots. For larger size, C, S, and vortex states may exist. The vortex state can stably exist from small diameter to large one both in square dot and circular dot. In circular dot, only one of the C and S states can exist for one given diameter and in some diameter range, none of the quasiuniform∕flower, C and S states can exist. Only the vortex state can be stable in this range. In square dot, C and S states can simultaneously exist, which are very different from the case in the circular dot.

Two different magnetization reversal processes, which are caused by the helicities of the two small vortex domain walls in the two sides of the onion state, are found numerically to exist in thin film rings. When the two vortex domain walls are in the same helicity, the onion state will transform to flux closure state (vortex state) with increasing of the field, and then transform from the flux closure state (vortex state) to the reverse onion state with further increasing of the field. When the two vortex domain walls are in opposite helicities, however, with increasing of the field, the onion state will transform directly to the reverse onion state skipping the flux closure state (vortex state).

The size dependence of reversal mechanisms and the corresponding switching fields of elliptical Permalloy thin films are studied by micromagnetic simulation. From the simulated spin configurations, it is shown that for ellipses with different dimensions there exist three reversal mechanisms: the buckling-instability mode, the vortex-propagation mode, and the mixed mode of buckling-instability and vortex-propagation modes.

Field evolution of vortex and cross-tie states is investigated by magnetic force microscopy imaging experimentally. We found that the vortices move perpendicular to the field direction. For the multivortex states, as the external field is perpendicular to the magnetization direction of the rhombic domain, which is enclosed by two neighboring vortices, the rhombic domain tilts. When the external field is parallel/antiparallel to the magnetization direction of the rhombic domain, this domain is extended/contracted. For the cross-tie state, the vortex and antivortex cores annihilate pair by pair in series when the field is applied along the short axis. When the magnetic field is applied along the long axis, the Bloch line moves along the short-axis direction till it, as a whole, annihilates near the edge of the elliptical thin film.

A metastable state for the elongated Permalloy elements is found to exist within a short field range before magnetization reversal. From the micromagnetic simulation it exhibits a wavelike structure, and the corresponding magnetic pole density distribution shows a pattern with periodic spots along the boundary. We also use magnetic force microscopy imaging and magnetoresistance measurement, which measures the nucleation field and coercive field, to study the noncoherent magnetization reversal properties of Permalloy ellipse with long axis, short axis, and thicknesses of 18μm, 1μm, and 45nm, respectively. The metastable state before switching is found to be repeatable.

Magnetic properties of microstructured Permalloy thin film cross have been studied using magnetic force microscopy and magnetoresistance measurement. Three types of magnetization configurations formed within the junction area were observed, including two kinds of magnetic pattern having two inward and two outward magnetizations and one with three outward and one inward magnetizations. The presence of those variant magnetic configurations gives rise to an irreversible magnetoresistance behavior originated from the distinct magnetization history. Asynchronous magnetization reversal of each arm provides a chance to manipulate the magnetic pattern of the cross.

The magnetic structures and hysteresis loops of permalloy thin film arrays are investigated here using magnetic force microscopy and vibrating sample magnetometer. The strength of interparticle dipole interaction can be revealed by the number of single-domain pairs with antiparallel magnetizations when the array is relaxed from a strong hard-axis field. Besides, hysteresis loops obtained by vibrating sample magnetometer measurements show that arrays with narrower interparticle spacings have lower coercivities and remanences. The results obtained from vibrating sample magnetometer are in very good agreement with magnetic force microscopy imaging.

The size dependence of switching fields of permalloy rings is studied by micromagnetic simulations and by magnetoresistance measurements. Experimentally, the switching fields can be obtained from the discontinuities of the magnetoresistance curve. From the simulated hysteresis loops and the magnetoresistance curves obtained by experiment it is shown that the switching field from the vortex state to the reverse onion state increases considerably as decreasing of the lateral size or as increasing of the thickness. There is, however, no significant correlation between the ring size and the switching field from the onion state to the vortex state.